Electric-cord protector



Feb. 23 1926.-

s. D." BLACK ET AL ELECTRIC CORD PROTECTOR Filed May 19 1925 I "Patente-deb. 23, 19.26.

*i Vv1,574,020

YUNITED s'r-.4\ T.Es vPATENT OFFICE.

I SAMUEL DUNCAN BLACK' AND A LoNzo eALLoWAY DECKER, or BALTIMoRE CoUNTY, MARYLAND, AssIGNoRs To THE BLACK a DECKER MANUFACTURING COMPANY, oE

TowsoN, MARYLAND, A coRroRATroN or MARYLAND.

ELECTRIC-Conn rRoTECToR.l

Appuati'qn madam-19, 1923. serial No. 640,034.

'To allgwhom t may Concern.' Be it known' that SAMUELA DUNCAN BLACK and ALONZO GALLowAY DECKER, cltizens ofA A. the United States of America, both residents of the county of Baltimore, State of Mary-V 'land, .have invented certain new and useful i Improvementsin' Electric-Cord Protectors, of which the following is a specification.

The invention relates' .to portable electric apparatus,.particularly electric tools, and

other portable' electricdevices which are connected to a source ofy electricity by means of a flexible conductor referred-to as a c ord which permits the :tool or other portable device to be manipulated in such manner as ma be necessary to itsv use withoutinterferlng with the ow of current necessary to its Operation. y

The use of these devices subjectsthe cord I to many destructive stresses at the point Wherethe Conductor enters Athe apparatus f which eventually results in breaking the strands of the conductorI in the vicinity of' the point of connectlon of the flexible-conductor or cordto the tool. These stresses,

though they sometimesoccur as` direct pullsl on the cord most frequently occur in the form of side pulls and twists. Whatever the origin vof these side pulls and twists,`they result, in almost-every instance, in bending the cord sharply in the section immediately :lidjacent the point of attachment to the too Failure oflthe conductor at this point is so frequent on account of these sharp' bends and twists to `whichnthe cord is subjected that numerous-,means of protecting it have been devised. Some'fof these have become well known, such -as the expedient of wind- 40 ing spring wire about `the cord or enclosing 'it within a piece of rubber hose. In fact the present invention may be treated as an improvement on the-latter device.4

The applicants have, in numerous inprotecting device and. are familar with its defects. This type of protecting member or support, as now ingeneral use, consists ofv a piece of flexible rubber hose of substantially uniform internal and external diameter throughoutits length, the tube or hose being secured at one end to the tool "frame where it encloses the point of connection of the cord to the frame, the cord being thus enclosed for the full length of the hose.

Neither this device nor any other, which is known to the' applicants, has proved effective as aA protection for the Cord. The 'principal diiiiculty encountered withthe hose is that being of substantially uniform cross section, it voffers a uniform resistance to.

bending and subjects the cord to sharp twists and bends at the point where it leaves the end ofthe hose. These bends and twists are almost as sharp as they would be in the absence of such protection.

The percentage of failure ofthe cords at this point has been extensively reduced andfailure has been substantially eliminated by the improved device which consists of a rubber tube of gradually reduced cross section from a point adjacent the tool to its outer end, which end ortion is so reduced in thickness as to 'su stantially conform to the direction of the pull applied to the cord or to the direction of the cord, so that the cord is subjected to no sharp turns, twists or bends near the point of attachment to the tool, the tendency to such destructive application of the pulls onV thev cord being, on the contrary, completely eliminated by the tapered protectlng device, which, under the action of all stresses, forms itself and the end portion ofthe cord in a substantially uniform curve which is continuous with the direction of the cord and which affords complete protection against the destructive action described.

In the accompanying drawing: 'we have illustrated an Aelectric tool with a flexible conducting cord to which the protecting device of our invention is applied.

A In the drawing:

Fig. 1 is a cross-section taken on the axis of our tubular protecting member showing the conducting cord in elevation and a 1 portion of the tool handle in section. 45 stances, utilized the. familiar hose type of VFig'. 2 is a section on thelne 2 2, Fig. 1,1 looking tov the right, in said ligure.

' Fig. 3 an elevation ofl an electric tool ,supplied with the protecting device ofthe inomitted.

Referring to the drawings by numerals:

The tool handle or toolv casing 1, is pro- 'vided with a hole or opening at a convenient point to admit the cord orconductor, 3 enclosed in the protecting tube. ln the form of the invention shown, the end of the covered portion of the cord which contains two separately insulated wires, 5, the said end portion being duly enclosed in the protector 9, is introduced into the tool casing l through an opening 7 therein, the casing being provided at the side of said opening 7, with an oblong seat 8 whichintersects said opening 7, cutting oi a considerable arc at the side of said opening as shown.. The seat provides shoulders' at each side of said intersection, which-shoulders are provided with screw holes`13 to receive screws 14 holding a clamping block 15, which occupies Said seat, being pressed against the protector Yby the tension of said screws, clamping the protector tube and cord tightly in their relation .to the tool frame. rlhe thickened portion of the protector being thus in effect rigidly connected to the tool.

As aforesaid, the protecting tube or hose, 9, encloses the cord from and including the point of attachment to the tool to the outer end of the hose and is formed with a reducing taper from its point of attachment, 10, to its outerv end, 11, WhereA it may be provided with a suitable bead, l2, encircling its outer end to reinforce the tube at this point, it being understood that ythe taper is not necessarily uniform but the end portion of the hose is thin enought and flexible enough to assume the direction of pull of the cord and the part near the tool is thick and stiff enough to support the cord. As

, clamped it forms at the extreme Butt 10 a relatively rigid extension of the frame which gradually increases in flexibility toward the free end. ln the commercial form of the invention, with the small size tools as quarter inch drills, the protector is approximately seven inches long,`one inch inside the casing and six inches outside,l and about threequarters of aninch in outside diameter at v the butt, the walls being thickest at the 'butt and reduced gradually and=^uniformly toy. ward the'free end, the outside-dimension tapering toa half inch at the lfree end, so that the tube presents a graduated'resis'tanc'e to lateral stresses which increa-sesffrom the free end toward the butt, and the free end of the protector when the cord is tightened, as-

-Y sumes a curve which is continuous with the cord and tangent thereto. While it is not.

the intention of the applicants to limit the claim to exactly the proportions named, this example will serve as a general definition of the meaning of theterms elongated and gradually-tapered,'as used ,in the claim.

- An importantfeature of the invention resides in the provision of a considerable degree' of play onA the part of the cable or `cord tion as villustrated in Fig. 1.

3 relatively to the tube 9, the passage or opening through the tube, as shown in Figure l, being of considerablygreater diameter than the external diameter of the cable whereby'the cord is permitted to slide freely relatively to the tube, as both members bend in response to lateral pull on the cable, the play or freedom of the cords in the tube or protector providing for longitudinal motion of the cord within the cable to provide for the change in relation of the parts and the change of the ratio of the respective arcs of curvature assumed by the tube and cord as different degrees of lateral tension or applied thereto at dierent angles, it being, of course, understood that the difference in length between two parallel arcuate lines increases as the radius decreases, it being clear that if the radius is inlinitely long and the lines straight, there will be no such variation, and that as the sharpness of 'curvature increases, the variation in length between 'the two parallel curved members increases as already ointed out. This changel of curvature ten ing to produce relative longitudinalimotion of the cord relatively tothe tube, is compensated by the provision of a tube with an o ening larger than the diameter of the cord), so that the latter moves freely back and forth as the protector is bent at various angles.

lt will be easily appreciated that in this way the greatest possible protection to the cord against rupture on account of bending near the point of-attachment to the tool is afforded. In fact, the use of the apparatus shows that injun to the cord on this ac` count' at this point is substantially eliminated.

ln Fig. 4 we have showna protecting tube constructed in accordance with our inven tion in aslightly modified form in that the tube or hose is formed of layers of fabric and rubcber instead of being homogeneous rubber or similar or equivalentgcomposi- We have thus described specifically and in detail the manner of constructing and'applying the device of our invention infder that the nature and operation of the 'same may be clearly understood,'however, the specific terms tlferein are used descriptively rather than in a limiting sensethe scope of the inventionbeing defined Ain the claim.

What we claim and desire to secure by Lettersl Patent is: l

The combination with a conducting cord l,

and a portable electric tool to which the conductor is connected, of a cord protector consisting of an elongated tube ofwfl'exible material enclosing and fitting loosely'about the cord, permitting the cord to slide-'freely in the tube, the tube having'a gradual taper, the thicknessof the walls ofthe tube increasing toward the tool, the'gla'r'ger end` f the ta' vpered protector'being inserted in vthe Vtool casing which has an opening to receive the same, and clampin means for rigidly securr ing the large end o the protector tube in the tool casing, so that it forms a substantially l0 .at the end permitting the protector at this point to conform to the direction of the cord, the protector presenting a graduated resistance to lateral stresses, causing the portion of the cord within the tube to assume a smooth curved line continuous with the direction of the remainder of the cord.

Signed byv us at Baltimore, Maryland, this 17th day of April, 1923".

SAMUEL DUNCAN BLACK.

ALONZO GALLOWAY DECKER. 

